1. Field of the Invention
The present invention relates to Coriolis gyros.
2. Description of the Prior Art
Coriolis gyros (coriolis vibrating gyroscopes) fall within two classes, each corresponding to the oscillation mode utilized. The two classes are: (1) shape and bending oscillations (e.g. wine glass (HRG: “Hemispherical Resonator Gyroscope”), ring, bar); and (2) spring and mass system (e.g. Lin-Rot, Rot-Rot, Lin-Lin, wherein Lin-Rot means that the excitation mode contains linear movements (“Lin”) and the detection mode contains rotary movements (“Rot”). Rot-Rot and Lin-Lin are defined correspondingly.)
Such classes of Coriolis gyros have specific advantages and disadvantages with respect to vibration and acceleration sensitivity. The relative advantages and disadvantages of the two classes are discussed below.
1. Shape and Bending Oscillations
    Advantages: Externally closed useful modes (excitation and detection mode) are typical, i.e. such modes do not transmit forces and moments to the outside. They are therefore excited by neither linear accelerations nor vibrations with linear and/or rotary components. (“External” relates to the “surrounding area” of the substrate. Forces or moments can act locally on the substrate itself as a result of movement of mass elements or individual structures, but these cancel one another out overall). The substrate is mounted on a housing or a ceramic (a “mount”), e.g. by adhesive bonding or soldering. No forces or moments are transmitted to the mount by closed modes. However, this is true only if no manufacturing tolerances have to be taken into account.    Disadvantages: Most known structures require soft suspension (e. g. ring, bar; an exception is the so-called HRG (Hemispherical Resonator Gyroscope), which requires complex manufacturing processes due to its “true three-dimensional” form). Such structures are deflected relatively significantly when accelerations and vibration occur, leading to errors in many force transmitters (e.g. electrostatic force transmitters) and taps (e.g. capacitive taps). Also, quadrature compensation, i.e. “balancing-out” of the structure by an actuating element, is virtually impossible, since the required forces are too great.2. Spring and Mass Systems    Advantages: Two articles, one by P. Greiff, B. Boxenhorn, T. King and L. Niles entitled “Silicon Monolithic Micromechanical Gyroscope” (Tech. Digest, 6th Int. Conf. on Solid-State Sensors and Actuators (Transducers '91), San Francisco, Calif., USA, June 1991, pp. 966-968) and the other by J. Bernstein, S. Cho, A. T. King, A. Kourepins, P. Maciel and M. Weinberg entitled “A Micromachined Comb-Drive Tuning Fork Rate Gyroscope” (Proc. IEEE Micro Electromechanical Systems Workshop (MEMS 93), Fort Lauderdale, Fla., USA, February 1993, pp. 143-148 or DE 196 41 284 C1) disclose structures in which the resonant frequencies of the useful modes may be considerably lower than that of the other modes that can be excited by accelerations and/or vibrations, and produce a significant error signal. Modes that cause a significant error signal are, in particular, modes that influence the measurement signal of the detection movement. Modes that influence measurement of the excitation movement are typically less damaging.    Disadvantages: Vibration and, frequently, linear accelerations can excite one or both useful modes and therefore cause error signals.
Rotation rate sensors each having two pairs of individual sensors which oscillate linearly in antiphase and with a linear detection mode are described in EP 1515119 A1. WO 95/34798 describes a Coriolis gyro having two seismic masses and a detection mode which is based on a rotary oscillation of the two seismic masses.